For the last quarter century, medical doctors have used ultrasonic sound waves, i.e., ultrasound, for generating images of sites within a patient's body. More recently, medical researchers have used ultrasound to promote the healing and growth of internal tissues such as bone. In both imaging and healing applications, a device applies the ultrasound either externally or invasively with respect to the patient, and directs the ultrasound toward the desired site.
An ultrasound imager processes ultrasound echoes to form images of internal tissues and organs. Ultrasound echoes are reflections of ultrasound from a first tissue at a boundary between the first tissue and a second tissue of a different density than the first. The imager calculates from the relative echo reception time and amplitude the relative position of a tissue boundary and the relative density of the reflecting tissue. An ultrasound growth stimulator causes ultrasonic vibrations in a tissue to promote the growth or healing thereof.
Ultrasound waveforms are characterized by their parameters, such as ultrasonic frequency, pulse amplitude, pulse width, and pulse repetition rate. These parameters may vary with the application. As an example of such parameters for imaging applications, "Diagnostic Ultrasound", Bruel & Kjaer, Marlborough, Mass. discloses an ultrasound frequency of 2-15 megahertz (MHZ), a pulse width of 1-5 microseconds (.mu.s), and a pulse repetition rate of 1000 pulses per second (pps). As an example of such parameters for stimulation applications, U.S. Pat. No. 4,530,360, issued to Duarte, discloses an ultrasound frequency of 1.3-2 MHZ, a pulse width of 10-2,000 .mu.s, and a pulse repetition rate of 100-1000 pps. Typically, an ultrasound stimulation pulse is stronger, i.e., has a larger amplitude, than an ultrasound imaging pulse.
Existing ultrasound imaging devices, such as the ones disclosed in "Echo-Encephalography", J. M. Saba, Medical Electronics, Issue 5, and "Intraoperative Ultrasound Imaging of the Spinal Cord", G. J. Dohrmann & J. McRubin, Surgical Neurologist, Vol. 18, No. 6, Dec. 1982 Little, Brown, & Co., Boston, Mass. have an external ultrasound transducer connected to a processing circuit and image display. As a trained operator holds the transducer against the patient's skin (which typically has been coated with an ultrasound coupling gel), a view is displayed of the internal tissues toward which the transducer is directing the ultrasound. The operator may move the transducer to display the desired view or multiple views.
It may be difficult for the operator to keep the transducer properly positioned, especially if the patient moves. Often, a patient must move a part of his body while the operator takes a series of images of the part. For example, a patient may have to slowly bend over as the operator takes a series of spine images that will show how the imaged area reacts to movement.
Also, the size and complexity of such an ultrasound imaging device typically force a patient to travel to the device's location (typically a medical center) for treatment. This traveling may be particularly burdensome when a doctor orders that a series of images be taken over an extended period. For example, a doctor may order that images be taken twice a week for two months so that he can monitor the healing of a tissue site, such as a bone fracture.
Existing ultrasound growth stimulators apply ultrasound to the treatment site either externally or invasively. Examples of external stimulators include U.S. Pat. Nos. 5,191,880 and 5,103,806, issued to McLeod et al., which disclose applying ultrasound to a bone site using vibrating floor plates and chairs, transducers attached to the skin, isometric exercises, or electrical muscle stimulation. U.S. Pat. No. 4,905,671, issued to Senge et al., discloses generating the ultrasound in and transmitting it to a bone site via a water bath in which is submersed the portion of the body containing the bone site. U.S. Pat. No. 4,530,360, issued to Duarte, discloses applying ultrasound to a bone site with a transducer held against the skin. Examples of invasive stimulators include U.S. Pat. No. 3,874,372, issued to Le Bon, which discloses a device having a needle that is inserted through the skin to apply ultrasound to an internal treatment site. U.S. Pat. No. 1,466,730, issued to Adarich, discloses two pins that are inserted into a bone on opposing sides of a fracture. The pins protrude through the skin and apply ultrasound directly to the bone site.
The design of external stimulators may hinder or prevent the patient or operator from keeping the ultrasound focused on the treatment site for the required time period, which may be several minutes or hours. For example, Duarte teaches a treatment having a preferred duration of 10-20 minutes, with some treatments lasting up to 55 minutes. It is often very difficult for the patient or operator to hold an ultrasound transducer in a fixed position, or for the patient to hold a portion of his body in a fixed position, for more than several minutes. Also, stimulators such as vibrating chairs or electrical muscle contractors are often unable to focus ultrasound, and thus may stimulate tissue sites not requiring or unable to withstand such stimulation.
Furthermore, external stimulators often must generate ultrasound waveforms of greater-than-required amplitude for promoting growth of the tissue site. External stimulators require additional power to generate this larger amplitude. Also, these stronger ultrasound waveforms may injure the intermediate tissue. The greater amplitude counterbalances the attenuation of the ultrasound caused by tissue intermediate to the ultrasound source and the tissue site.
Invasive stimulators require direct access to the treatment site via an opening in the patient's skin. This opening is prone to infection and may cause discomfort to the patient, particularly when the stimulator remains installed for an extended period of time. Additionally, the foreign presence in the patient's body may cause him further discomfort.
Like the above-discussed ultrasound imaging devices, the complexity of both external and internal stimulators often forces the patient to frequently make burdensome trips to a medical center for treatment. Typically, multiple applications of ultrasound are required over the course of treatment. For example, Duarte teaches daily treatments for 30-45 days. Also, a trained operator is usually needed to operate such stimulators. Additionally, the invasive devices often require a doctor to insert them into and remove them from the patient's body. The use of some invasive devices may even require the patient to remain in the hospital during the course of treatment.